The May, 1994 Gordon Research Conference on Mitochondria and Chloroplasts in Volterra, Italy, will bring together an international group of geneticists, molecular biologists, biochemists, cell biologists, and clinical physicians to exchange ideas and information on a wide range of problems in these organelles. It will be the first international Gordon Research Conference on Mitochondria and Chloroplasts and the only meeting in this area since the last Gordon Research Conference in 1992. Organellar genetic systems are found in all eukaryotic cells. Investigations into their functions and regulatory processes are critical to our understanding of eukaryotic cell biology. Increasing evidence points to mitochondria in animals, and to mitochondria or chloroplasts in plants, as the underlying cause for clinical myopathies and plant diseases. In addition, several important processes that affect RNA processing and protein function have emerged from the study of animal, yeast, and plant mitochondria, as well as plant chloroplasts. This timely GRC Conference will promote the dissemination of novel information that will help to facilitate further research into organelle systems. Areas covered in depth during the 1994 Conference include the replication processes that lead to organelle mutations, examples of such mutations in both plant and animals (with two sessions devoted to mitochondrial myopathies and their phenotypic/clinical diseases), RNA editing processes and transport of RNA across organelle membranes, transcriptional and post-transcriptional regulation of organelle gene expression, transport and assembly of nuclear-encoded organelle proteins, and novel functions of organelle DNA and RNA. Significant new and exciting developments have occurred in all of these areas since the last Gordon Conference, and there is a high degree of enthusiasm among research for the 1994 Conference as documented by the fact that except for three invitees, all other speakers have accepted the invitation.